The present invention relates to a method for enriching and separating heavy hydrogen isotopes, namely deuterium and/or tritium, from substance streams containing such isotopes, wherein the respectively present hydrogen isotopes are exchanged in chemical equlibria.
One method for enriching hydrogen isotopes by isotope exchange is disclosed in DE-AS No. 2,728,576, wherein the isotope exchange between liquid water and gaseous hydrogen is effected in the presence of a catalyst mass comprising a suitable carrier, at least one metal from Group VIII of the Periodic Table and a hydrophobic polymer material which is permeable to water vapor and hydrogen gas. Initially, there occurs a catalytic isotope exchange between hydrogen gas and water vapor, and thereafter there occurs, in a noncatalytic process stage, an isotope exchange between water vapor and liquid water. This process employs a catalyst mass in which additional packing components are dispersed and can be used for the enrichment of deuterium, and also of tritium.
The exchange process described in De-AS No. 2,728,576 is connected with high expenditures for controlling it as well as for the size of the plant required to implement it and for the energy consumed by it. It operates with a stream of hydrogen and cannot be simply transferred to processes which are to be integrated, for example, into a process like the Purex process for reprocessing of irradiated nuclear fuels.
A process for purifying the product solutions of tritium obtained during reprocessing of irradiated nuclear fuels according to the Purex process is disclosed in published European Patent Application No. 0,023,530. This purification process operates with a plurality of series connected extraction cycles employing an organic solvent and is characterized in that a plurality of intermediate purification cycles of the aqueous phase are provided for the extraction of tritium. The recovery of uranium and/or plutonium during reprocessing of irradiated nuclear fuels is effected in several extraction and re-extraction cycles in which aqueous waste solutions are obtained which contain tritium in the form of HTO. An intermediate purification cycle of the aqueous phase for the purpose of extracting tritium begins in the second extraction stage of the actinides and leads back to the first re-extraction stage. The aqueous phase is extracted in the second extraction stage and caused to evaporate.
From there, the concentrate containing HTO is removed and is extracted from the intermediate cycle. The distillate is then mixed with a freshly started solution containing the required chemicals, but not yet containing tritium, and is introduced into the first re-extraction stage so that the intermediate purification cycle is closed.
The tritium purification process described in European Patent Application No. 0,023,530 results in only a relatively low enrichment of HTO and requires a large amount of energy for the evaporation of the aqueous phase from the second extraction stage.